1. Field of the Invention
The present invention relates to a router device for forwarding a communication packet.
2. Description of the Background Art
The total traffic volume that can be transferred over a telecommunications network is an indicator for measuring the performance of the network, and is important. In order to increase the total traffic volume, Zhen Yi Chen et al., “Effects of network structure and routing strategy on network capacity”, PHYSICAL REVIEW E, 73, 036107, 2006, The American Physical Society, proposes a method for forwarding packets by a router. Zhen Yi Chen et al., proposes the method including consideration of the number of hops to a destination address and queue-waiting time. This can avoid congestion in routing. The steps for routing (1) and (2) will be described below.
(1) A router intending to forward a packet, when selecting a next router to which the packet is to be transmitted, calculates a weight Hi for each neighboring router i through an expression (1) representing the cost incurred when the packet passes the node i,
                                          H            i                    =                                    α              ⁢                                                          ⁢                                                E                  i                                                                      ∑                                          j                      ∈                                              g                        ⁡                                                  (                          i                          )                                                                                                      ⁢                                      E                    j                                                                        +                                          (                                  1                  -                  α                                )                            ⁢                                                L                  i                                                                      ∑                                          j                      ∈                                              g                        ⁡                                                  (                          i                          )                                                                                                      ⁢                                      L                    j                                                                                      ,                  0          ≤          α          ≤          1                                    (        1        )            where g(i) is a set of neighboring routers of the router i, E(i) is the queue-waiting time of the router i, and L(i) is the number of hops from the router i to a destination address. When a packet passes the router i, the first term in the right-hand side of the expression (1) represents a temporal cost for processing the packet, and the second term represents a distance cost for sending the packet to its destination address.
(2) The router forwarding the packet selects a neighboring router having the minimum weight Hi through the above expression (1) as a next router to forward the packet thereto. The account of the temporal cost thus taken can accomplish routing with a congested router requiring long time for processing the forwarded packet avoided.
According to these steps, compared with routing protocols such as RIP (Routing Information Protocol) or OSPF (Open Shortest Path First) for routing simply with the number of hops to a destination considered, the total traffic volume of a network can be increased.
The forwarding method described in Zhen Yi Chen et al., requires neighboring routers to be notified of the queue-waiting time. However, if all the neighboring routers are notified of the queue-waiting time by packets, they would have to process those packets to incur an increased load thereon, thus congesting the traffic on the network.
Moreover, the expression (1) also involves a matter of determination of the parameter α defining how much the ratio between the queue-waiting time and the number of hops is to be reflected on the weight Hi. Zhen Yi Chen et al., discloses that the value of parameter α maximizing the maximum value λcrit of the amount of packets which the router as a constituent element of a network is capable of generating per unit time depends upon the topology of the network. This means that since the value of parameter α maximizing the total traffic volume of a network is thus dependent upon the topology of the network, the determination of the optimum parameter α requires to learn the topology of the entire network in advance.
Well, although Zhen Yi Chen et al., teaches the parameter α maximizing the total traffic volume of a specific network topology, it is silent about how to determine the parameter α for an existing network. Therefore, in the case of applying a routing method with the parameter α fixed to an actual network, when it is taken into account that the value of parameter α maximizing the total traffic volume of the network is dependent on the topology of the network, the determination of the parameter α requires to know the topology of the entire network. However, such a method is not practical.